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United States PatentO flee MEMORY sELEcTrNo SYSTEM John F. Donau, Reseda, Daniel J. Daugherty, Torrance,

and Willis E. Dobbins, Manhattan Beach, Calif., assgnors to The National Cash Register Company, Dayton, Ohio, a corporation of Maryland Application August 17, 1954, Senal No. 450,291 1t) Claims. (Cl. 340-174) This invention relates to the process of searching the memory of a digital computer for a designated storage portion thereof and more particularly to means for reducing the average time required for the arithmetic unit of a digital computer to communicatev with a particular storage register on a rotating drum memory.

A general purpose digital computer is designed to manipulate data susceptible to representation by digital techniques. Such data takes the form of a problem which in computer operation is reduced to a rather extensive routine by means of appropriate programming. This routine often requires the repetition of 'an operation, auxiliary to the actual computation, which, although of relatively short duration, may cumulatively expend operating time far in excess of that Vtaken by the computer to perform the actual computation. Probably the most frequently occurring of such repeated auxiliary operations is that of look-up which involves for example, searching the drum memory for a particular address and transferring the information stored therein to an arithmetic register of the computer where it may be appropriately handled in subsequent operations, and then returned to the drum memory by a similar look-up operation. This process requires a period of time commonly designated as access time. For a particular cyclic system, of which a magnetic drum computer is representative, access time is primarily a function of the time lapseV between successive appearances ofthe same storage address on the drum at a location where information can be either Since access time ,comprisesI an appreciable lportion of computer operating time, `and is consequently a factor in the cost of operating the computerit is apparent that it is highly desirable that it be minimized.

Briefly, the preferred embodiment of the present invention accomplishes a` reduction in access time required by a computer to communicate with its memory by the employment of a plurality of equally spaced heads about each of the channels of the computer magnetic drum memory, together with logical circuitry which selects the head next to be operatively in a position to sense information from or record information into the desired storage register. Assuming a particular channel is already selected, the process of head selection involves a subtraction of the coded decimal numbers representing the arc addresses of the storage register, as read by the head associated with the arc address channel on the drum, from the arc address of the desired storage register, as stored in a recirculating register cooperating with the arithmetic unit. Immediately upon electing this subtraction process, a numeral designating the proper head to be used is determined; and, assuming information is to be read from the memory, the output of this head is gated so as to be made available at the arithmetic unit to the exclusion of the others. Since there are several storage'registers provided between successive heads of the channel, simultaneous with this head selection, further circuitry is pro- 2,935,734 Patented May 3, 1960 address channel with the arc address of the storage register desired. It is not until this comparison is effected that the arithmetic unit is enabled to sense the signals passing the gate previously selected which correspond to the desired storage register.

It is thus an object of this invention to provide an improved computer memory system wherein the time required for communicating with a particular storage register on the memory is minimized.

Another object of this invention is to provide electrical components and circuitry to accomplish a gated and timed selection of one of a plurality of magnetic heads situated around the periphery of a drum memory.

A further object of this invention is to provide a novel computer magnetic drum storage system operable in accordance with bistable state elements responsive to logical networks capable of being dened in the notation of Boolean algebra.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the preferred embodiment detailed in the following description and the accompanying drawings wherein:

Fig. 1 is a perspectiveview illustrating the cooperative relationship of relevant portions of the computer system exemplifying the present invention.

Fig. 2 shows the code pattern employed -during a Word period to represent a command.

Fig. 3 shows the code pattern employed during a word period to represent a number.

Fig. 4 illustrates one word period of the arc address channel showing how the code pattern of a particular arc address is recorded thereon.

Fig. 5 presents the arrangement'of the address specifyingthe storage register desired as stored in the H recirculating register.

Fig. 6 shows in particular a diagramv of the memory channel gating circuits provided for one of the memory channels on the ldrum and the relation thereof to the arithmetic unit.

Fig. 7 is a circuit diagram of the channel selector matrix for the memory channels.

Fig. 8 is a table showing the states of the channel selec Y tor dip-flops, U9 to U12.

vided for comparing the arc address as read from the arc Voperation of'lip-flop K3.

Fig. 15 is a block diagram of adder-flip-ops A13 to A16, together with the logical equations defining their operation.

Figs. 16, 17, and 18 are tables illustrating the derivation of the logical equations defining the operation of the adder input flip-flop A13, and the carry tlip-ops K1 and K2.

Fig. 19 is an electrical diagram of the ltrigger input equation networks for the A13 to A16 dip-flops.

Fig. 2.0 is a block diagram of adder carry nip-flop K1 together with the electrical diagram of the diode networks for generating its trigger input equations.

Fig. 21 is a block diagram of tixup adder carry Hip-flop K2 together with the electrical diagram of the diode networks for generating its trigger input equations,

Fig. 22 is a portion of the functional flow diagram of the computer relevant to the look-up process.

Fig. 23 shows an example of how head identification is performed by the computer for the condition characterized by the excess 6 sum having a carry-out.

Fig. 24 shows an example of how` head identification is y.performed by the computer for the condition characterized by the excess 6 sum not having a carry-out.

Fig. 25 shows an example of how head identification is performed by the computer for the condition where the desired arc is passing a memory channel head at the instant the look-up process is initiated.

Fig. 26 is a block diagram of iiip-op Nd together with the electrical diagram of the diode networks for generating its trigger input equations.

Fig. 27 is a block diagram of flip-flops U9, U10, etc. comprising the channel selector register together with an electrical diagram of the diode networks for generating their trigger input equations.

Fig. 28 is a block diagram of ip-ops U13, U14, etc. comprising the head selector register together with an electrical diagram ofthe diode networks for generating their trigger input equations.

The embodiment herein disclosed is intended as part of a general purpose computer. It is to be noted that this specification and the accompanying drawings will describeand illustrate in detail only such portions of the computer as are directly concerned with the present invention and are necessary to explain the principle thereof.

Referring first to Fig. 1, an overall pictorial view of the portions of the general purpose computer relevant to the invention is presented. Here is shown a memory drum 101 provided on the surface thereof with a plurality of storage registers comprising arcs or portions of circumferential channels, such as storage register 141. Also is shown an arithmetic unit 103 which operates integrally with the 4drum 101 by way of G and H recirculating registers 116 and 117, respectively. In addition, here is shown clock counter 102, gating unit 104, program counter 105, and interconnecting lines intended to be representative of functional cooperation between these components; It is to be notedthat the components in Fig. l are not to be considered physically unique but are to beconsidered separate only from a functional viewpoint and have been arranged as shown for the purpose of explaining the invention. It is in this regard that they will be described. For example, arithmetic unit 103 and gating unit 104 may employ circuitry in common and thus a description of this circuitry will consider only its function when so used and not define it as a physical part of either unit.

Memory drum 101 is supported on suitable arbor mounts 106 and a base plate 107 and is rotated in a clockwise direction, as indicated by the arrow on its left end, by motor 108 through drive shaft 109. Deposited on the surface of drum 101 is a coating 110 of magneticmaterial, such as ferrie oxide, which enables information to be stored as magnetic patterns thereon. Shown stationarily positioned to have a working relation with coating 110 are a plurality of sensing elements, such as head 111 which is responsive to magnetic signals recorded on a clock channel 112. Thus it can be seen that as drum 101 rotates, circumferential channels, spaced along the drum longitudinal axis, are effectively described thereon by the stationary heads. There are, in addition to clock channel 112, ten main memory channels 113 and an arc address channel 114. It will be noted that clock channel 112 and arc address channel 114 each have but one head associated therewith, whereas the ten memory channels 113 are each provided with ten equally spaced heads.

Commencing from the( left end of the drum 101, the first channel shown is clock channel 112, which has associated therewith clock head 111. Clock channel 112 completely circumscribes drum 101 and contains a perma nently recorded magnetic flux pattern representing an electrical sinewave so as to form a closed loop. Each cycle of this sine wave defines an elemental memory area on the drum periphery on which a binary bit of information may be recorded. Thus the signals on clock channel 112 divide the drum circumference into a fixed number of such elemental areas; namely, 4400 in the present computer. Clock head 111 is stationarily positioned close to the drum periphery and senses the changes in magnetic fiux pattern, thereby generating an electrical signal indicative of each sine wave cycle. In construction, clock head 111 is comprised of a split core of soft iron or a like conductor of magnetic lines of force, and a coil wound thereon, in which the electrical sine waveform is induced as the magnetic flux on drum 101 moves past the core gap. One terminal of the coil is grounded and the other terminal is connected to circuitry designed to shape the induced voltage preliminary to causing it to serve as a driving voltage for other components.

ilt has already been noted that interconnecting lines between computer components of Fig. 1 are intended to be afunctional representation of cooperation therebetween and may actually comprise not only connections but also circuitry and equipment. A consideration of clock line 126 will exemplify. Although clock channel 112 is impressed with a pattern resembling a sine wave, the clock input to clock counter 102 and arithmetic unit 103 is a symmetrical square Wave, the period of which is equal to that of the original sine wave and the amplitude of which is Yclamped between v. D.C. and +125 v. D.C. This square wave will be referred to hereinafter as clock proposition C (see Fig. 14 line I), and the time period between trailing edges of clock proposition C will be designated one clock period. Additionally, the half of clock proposition C which is at the potential of v. D.C. will be referred to as the clock pulse, since it is the trailing edge of this half onlywhich triggers logical circuitry in the computer.

Circuitry which effectuates the change from sine wave to clock proposition C is driven by the output of clock head 111. As Vpreviously stated, this circuitry is schematically represented in Fig. 1 by clock line 126 and may comprise several stages of amplification, a pulse shaping circuit, a triggering circuit of the Schmidt type, and a diode clamping arrangement, as already disclosed in the prior art. The clock proposition C thus provided is used for synchronizing logical networks of arithmetic unit 103 and to drive clock counter 102. It'should be understood that all logical propositions in the computer operate at the same two voltage levels as clock proposition C, i.e., +100 v. D.C. and +125 v. D.C.

It is by utilizing the signals induced by clock channel 112 as a reference during reading andrecording that the computer effectively divides the otheicircumferential channels of drum 101 into asimilar number of elemental memory areas and also snychronizes theoperation of all circuits so that they operate in accordance with a basic timing logic. Each of these elemental memory areas on the periphery of drum 101 in the other channels shown in Fig. 1 is capable of containing a digit of binary information, i.e., a saturated flux pattern either in one direction or the other. When the flux is in one direction in a given elemental memory area, a binary digit one is represented; when it is in the other direction, a binary digit zero is represented. Since the non-return-to-zero method of storing information on the drum is employed, the recorded flux pattern changes for successivermemory areas only when the binary digits of asequence change from 0 to 1, or vice versa.

Computer components are designed to serially handle information in blocks consisting of a fixed number of. binary digits. These blocks may represent either commands or numbers and are commonly referred to as words A word is comprised of a sequence of 44 consecutive binary digits and thus requires 44 consecutive memory areas for storage. The portion or arc of a circumferentialchannel in which a word maybe recorded,

such as 4arc 141 of Fig. 1, is designated a'storage register. Since clock channel 112 contains 4400 clock signals, 100 such storage registers are provided along the circumference, that is, on each channel, of drum 101. As shown on the left end of drum 101 in Fig. l, each of the arcs occupied by a storage register, such as arc 141, is assigned an arcuate address, through 99, running consecutively in a counterclockwise direction such that the heads sense information in successive arcs of higher number except for thediscontinuity when arc 99 is succeeded by arc 0. The time required forv one arc to pass a head is designated as one word period which is defined by 44 cycles of the sine wave passing clock channel head 111.

In order to enable arithmetic unit 103 to properly respond to and identify each of the digits in a storage register being sensed at any given time, clock counter 102, comprised of P counter124 and D counter 125, is provided for counting successive clock periods. Clock counter 102 responds to 44 clock periods to define each word period. P counter 124 respondsY directly to the output of clock line 126 (i.e., to clock pulses) and has a capacity of four counts, namely, PO, P1, P2, and P3, before it resets. A carry pulse generated once each cycle of P counter 124 (i.e., at the end of the P3 pulse) causes D counter 125 to manifest a new count throughout the next cycle of P counter 124. The capacity of D counter 12S is 16 counts of which the computer employs 11, Le., although D counter 125 can count to 16, it is forced to reset to zero after the eleventh count.` The counts of D counter 125 are designated DO, D1 D10 and with counts of P counter 124fa'reV manifested by signal outputs feeding into arithmetic unit 103 such that, as drum 101 rotates and an arc or storage register is being sensed by the heads, succeeding elemental memory areas of the arc, hereinafter to be designated pulse positions, are identified by clock counter 102 as DOPO, DOP1, DOPO, DOPO, DIPO D1OP3. In summary, each word period is divided by this arrangement into eleven D (digit) periods each of which is subdivided into four P (pulse) positions and in each of the latter may be stored one binary digit of a binary-coded decimal digit. Accordingly, by noting the counts in clock counter 102, the pulse position in an arc, or storage register, presently being scanned by the heads on drum 101 can be observed.

The means employed in clock counter 102 to dene any pulse position or combinationof pulse positions of a word, so that circuitry in arithmetic unit 103 may be yarranged to provide proper triggering for ip-ops as required by their respective equations, is well understood in the prior'art. Thus, considering P counter 124, Fig. l indicates that two flip-Hops, B1 and B2, are employed. The arrangement is a parallel one in that clock proposition C is simultaneously applied to all gates associated with the inputs to these ip-ops. The interconnection of the outputs, however, allow the flip-flops to' be triggered by successive clock pulses only to change their states to indicate the P cyclical counts. It is well known that there are four possible different arrange' ments of two flip-flops and here each of the counts PO, P1, P2, and P3 represent a different configuration of iptlops B1 and B2. The arrangement for D counter 125 is similar, and each of the counts DO, D1 DIO represents a different configuration of ip-iiops B3 through B6. Depending upon the pulse position of an arc tov be represented, a particular configuration of each of the two groups B1-B2 and 13S-B6 is routed to arithmetic unit 103 during each clock period generated by clock line 126, etfectuating a ditterent arrangement in a matrix type of diode network, the eective output of which is used as an input to logical gates or mixers.

The configuration of computer words and the -representation of decimal numerals employed by the computer will next be discussed as preliminary to a description of the other channels of drum 101. The computer employs :the excess 3 binary number system. It is well understood that the excess 3 binary number system requires the use of four binary digits to represent a decimal digit. Thus, by referring, for instance, to Figs. 2 and 3, which show the computer word representations of a command and a number, respectively, it can be seen that an entire D period is required to store a decimal digit. Considering Fig. 2 first, it is seen that the command represented in general notation therein is divided into eleven D periods, marked DO through DIO from right to left, while each D period is further divided intol four P positions. The information in a command is defined by the general notation 11, m1, m2, m3, where m1, m2, and m3 represent addresses (arc and channel) of arcs or storage registers in the tenA memory'channels 113, and I1 corresponds to an instruction to be carried out by arithmetic unit 1 03. Each of the sections m1, m2, and n3 of the command is in turn divided into two portions, such as m2a and mzc for the m2 address. The superscripts a and c characterize that information in theseportions are descriptive of the arc address and channel 1address,`respectively, of an arc on drum 101. Hence mz, located in periods D4 and D5, comprises binary-coded excess 3 numerals representative of any of the arcs 0 through 99; and mzc, located in period DO, comprises a binary-coded excess -3 numeral representative of any of the ten main memory channels 113, hereinafter defined as Ch0 through Ch9 inclusive. It will be noted that when the computer places a Abinary-coded excess 3 numeral in a D period, the least significant binary digit of the numeral occupies the PO position and binary digits of successively greater significauce occupy the positions P1, P2, and' P3, respectively. Also, the least significant decimal digit of a decimal numeral is placed in the lowest order D period of those assigned to the decimal numeral.

With regard to Fig. 3, here it is shown that the arrangement for a number is divided into D periods and P positions similar to the arrangement of Fig. 2. The computer provides for operating on decimal numerals 9 digits in length, to which binary numerals 36 digits in length contained in periods D1 through DO are equivalent. The DIO period of the number contains coded information indicating whether the sign of the numeral is positive or negative and whether or not a carry digit beyond the most significant digit of the numeral has been obtained as a result of the preceding computation. It will be noted that, in accordance with the rotation of drum 101, the lirst position of a word to pass a particular head is the DOPO position.

` Returning again to Fig. l and continuing with a description of the other channels on drum 101, next in order from the left end thereof are the ten main memory channels Ch0 to Ch9, inclusive. The information in main memory 113 is comprised of words constructed as aforementioned, on which and by which the computer operates. Each main memory channel is equipped with ten stationary memory heads, designated Hd0 to Hd9, inclusive, spaced at equal intervals along the channel. These heads are used for both reading and recording. Thus there are ten arcs or storage registers between successive memory heads of a memory channel and ten word periods are required for a particular storage register to traverse the distanceV from one memory head to the next. All memory heads bearing the same identifying numeral are precisely aligned (time-wise) along the drum longitudinal axis and thus sense information in similar memory areas of the arc of the same numeral but in dierent channels. Stated another way, Hdtl of Ch0 is sensing the contents of the tirst .elemental memory area of arc 22 in Ch0 at the same instant that Hd0 of Ch9 is sensing the contents of the first elemental memory area of arc 22 in Ch9. Since,l in this computer, there are 1G memory channels and 100 arcs or storage registers available on each, a total of arcs or storage registers are provided for storing words. Thus the capacity of drum 101 for storage is 1000 words;y and a coder, in setting up a problem, may use ases-ree any portion thereof. As shown`in Fig. 1, information sensed by all memory heads is supplied to gating unit'104.

`The next channel on drum 101 is arc'address channel 114. Each of the arcs of this channel contains a permanently recorded magnetic pattern representing the binary-coded excess 3 numeral equivalent of a decimal unit more than the decimal numeral which has been assigned to the arc, as indicated at the left end of drum 101 in Fig. 1. Associated with arc address channel. 114 is head 115, which senses the code of each arc address as drum 101 revolves. It should be noted that here arc address head 115 is shown precisely aligned with the memory heads Hd0, although this alignment is not required provided that the information encoded in the arcs yof arc address channel 114 indicates a decimal unit more than the numeral corresponding to the arc actually passing the memory heads Hd0.l In other words, when arc 22 is being sensed by the memory heads Hd0, it is essential that the output of arc address head 115 represent the binary-coded excess 3 equivalent of the decimal numeral 23. Referring to Fig. 4, a diagram of a portion of the arc address channel 114, defining in particular arc 23, is shown. In eachpof the arcs of arc address channel 114 corresponding to the maa portion of a word (i.e., in the D45 period), signals representing the binarycoded excess 3 numeral indication of the decimal numeral assigned to this are are permanently recorded. In the computerAlook-up operation, the present invention provides means to cause arithmetic unit 103 to subtract the arc address, as read from the arc address channel, from the desired arc address as stored in the D4 5 portion of the H recirculating register, to obtain a numeral representative of the memory head next to be passed by the desired memory channel storage register as drum 101 revolves. Simultaneously, arithmetic unit 103 compares corresponding digits as read from the arc address and the H recirculating register during D4 time to determine the word period during which this selected memory head will be passed by the desired arc. As shown in Fig. l, the binarydigits read from the arc address channel are serially set up in ip-ilop Wc. It should be noted that the details of the circuitry for serially triggering Hip-flop Wc, in accordance with the magnetic pattern on the arc address channel, have already been disclosed to the art. Briey, the binary squarewave pattern impressed in arc address channel 114 is sensed by arc address head 115 and, due to differentiation thereby, presents pulses representing the leading and trailing edges of the square wave. These pulses are amplified, clipped,` clamped between the limits +100 v. D C. and +125 v. D.C., and applied to the grid input circuits of flip-flop Wc, through a diode gate such that the leading-edge pulse triggers the flip-flop into one state and the trailing-edge pulse triggers the ilip-flop into the opposite state. The grid input circuit diode gates of ip-flop Wc are synchronized with the clock periods by application of thc clock proposition C from clock line 126. These concepts will be further clarified later in connection with the convention adopted to present the computer logic. The output of hip-flop Wc provides one of the inputs to diode network 137 of arithmetic unit 103, as will also be shown hereinafter.

Still referring to Fig. l, at the right end of drum 101 are shown the G and H recirculating registers 116 and 117. Each of these recirculating registers has two heads associated with the drum memory, one for reading and the other for recording, arranged such that as drum 101 rotates, a portion of the drum surface will pass the record head first and the read head later. Thus the H recirculating register includes a read head 121 spaced along the `drum surface ahead of arecord head 119, and the G recirculating register includes a read head 120 spaced along the drum surface ahead of the record head 118. Thus, as far as the recirculating registers are concerned, only a small arcuate portion of the drum `surface is used for storing information ata-given time. Theportion-used occupies Van area equivalent to less tlran'44 elemental memory areas, and the information is delayed in arithmetic Vunit 103 a given number of pulse periods so that the normal recirculating time for each register is 44 clock periods, i.e., one word period. Both of the G and H recirculating registers have their heads interconnected by way of the arithmetic unit 103 so that, for example, when the computer circuitry is set for recirculation in the G register, a particular unit signal on being recorded on the drum surface by record head 118, willv be carried by the revolving drum 101 to read head 120, sensed thereby, transmitted to arithmetic unit 103 wherein the signal steps through flip-flop circuits, and is then retransmitted to record head 118 by which it is again recorded. As previously stated, the design of the computer is such that the normal total time required for a particular digit to make one such cycle in the G register or in the H register during normal recirculation is equal to one word period. This is true even if it is desired that this digit undergo a modification. Fig. 5 illustrates the content of the H recirculating register, deiining in particular channel Ch8 in the D6 period thereof and arc 75 in the D4 5 period thereof.

It should be understood that the read and record circuitry for the G and H recirculating registers is well understood in the prior art. Briey, as shown in Fig. l1, the output of diode network 137 of arithmetic unit 103 for the G register, designated as proposition G0 (H0 in the case of the H register), is a square wave clamped between v. D.C. and +125 v. D.C., and is fed to the gating circuit of one grid of flip-flop G2 of Fig. 1 and, after inversion, is fed as proposition G0 to the gating circuit of the other grid of flip-flop G2. Both grid gates are synchronized with clock pulses by clock proposition C as heretofore mentioned. The outputs of flipop G2, namely, G2 and G2', are represented by line 122 and are employed to energize record head 118.

In the computer the processes performed are all divided into sequential steps or time periods of one word duration known as word periods. This is also the time required for information to normally circulate in the G recirculating register or in the H recirculating register. It is the function of program counter to render certain computer circuitry operable at the proper time so as to accomplish each such step operation. Accordingly, program counter 105 generates a plurality of output signals PC#0, PC#1, etc., each of which selects certain networks to respond to the desired inputs during each of the 44 clock periods of a word to generate the desired output propositions. Precisely at the end of each word period, the content of program counter 105 may or may not be affected, depending on the state of a decision component, namely, ip-op Nd, during the last, or Dwla period of a word. If flip-flop Nd is true during D10P3,

` program counter 105 is caused to count to the next higher count, whereas if llip-tlop Nd is false during D10P3, program counter 105 is caused to remain in the same count for another word period thus repeating the wordlprogram just completed. It follows that if program counter 105 counts, other circuitry of diode network 137 becomes operable commencing at DOPO of the next word period, but if program counter 105 remains unchanged, the circuitry of diode network 137 yis not affected during the next Word period.

The circuitry corresponding to a particular count of program counter 105 is made etfective in accordance with the states of the flip-flop N1 through N9. The arrangement adopted by the program counter is defined by trigger logical equations for each of the grids of Hipilops N1 through N9 in accordance with the various functions to be performed. The flip-flops are interconnected by a logical counting network causing them to operate as a binary counter whose outputs indicate PC#s, as taught in the prior art. Since flip-flop Nd is controlled inA turn by circuitry of arithmetic unit 103, .it

. 9 is apparent that mutual control occurs between program counter 10S and arithmetic unit 103.

It has been pointed out that all memory heads supply information to gating unit 104. More specifically, the outputs from the 100 memory heads are fed simultaneously into gating unit 104 where only one of such outputs is selected at a time in accordance with signals from arithmetic unit 103 received over gate input line 127. The selected head output is transmitted from gating unit 104 via gate output line 128 to arithmetic unit 103 wherein memory read flip-flop Mc is caused to respond thereto. The action will be made apparent by reference to Figs. 6 through 10 in conjunction with Fig. 1. A set of flip-hops (U9 to U12) in arithmetic unit 103 is arranged to function as channel selector register 142, and another set (U13 to U16), also in arithmetic unit 103, is arranged to function as a head selector register 143 during the time that the memory is being searched. Both of these selectors, 142 and 143, cooperate to send a selective signal through gate input line 127 to gating unit 104. This signal causes gating unit 104 to pass information from only one head through gate output line 128 to flip-hop Mc in arithmetic unit 103. Referring to Fig. 8, a table shows the contents of the channel selector hip-flops which defines the outputs for each of the memory channels; while Fig. 7 shows adiode matrix which reduces these defined outputs to physical circuitry. Similarly, Fig. 10 is a table showing the contents of the head selector flip-flops which characterizes the outputs for each of the heads of a memory channel, whereas Fig. 9 shows a diode matrix which reduces these defined outputs to physical circuitry as well as combining them with the outputs of Fig. 7 to produce combination outputs representing the selection of a particular head on a particular memory channel.

Thus note that output Ch in Fig. 7 is connected to a common line 168 to which inputs designated U9', U10', Uu, and U12 are connected by diodes, such as diode 169. A +225 v. source is also connected to common line 168 through a load resistor 170. The operation of this circuit is such that only when all of the inputs to common line 168 are at the high potential of +125 v. that the output Ch0 is at substantially this same high potential. The matrix of Fig. 9 operates in a similar manner. Each of the inputs to common line 168 can have either a high potential of +125 v. or a low potential of +100 v. Thus, only one of the output lines from the diode matrix shown in Fig. 9, such as Ch0 Hd0, will be at the effective potential of +125 v. D.C. at any one time while all other output lines (Ch0 Hdl, Ch0 Hd2 Ch9 Hd9) will be at the ineffective potential of +100 v. D.C. It will be noted that all the diode networks in the computer are operated at the same potentials as the diode matrices of Figs. 7 and 9, namely, +225 V. D.C. and ground. It will be noted that the matrices of Figs. 7 and 9 are composed of a plurality of diode gating circuits, hereinafter to be discussed in detail.

Fig. 6 details the circuitry in gating unit 104 for routing information between memory channels 113 and arithmetic unit 103, showing in particular a cross-section of drum 101 at channel Ch0. With reference to Hd0, coil 135, in which is induced electrical pulses as the substantially square magnetic saturation pattern on Ch0 moves past Hd0, is connected atA one end to the control grid of tube 134 and at the other end to line 127 and thence to Ch0 Hd0 of Fig. 9. The cathode of tube 134 is maintained at +115 v. D.C. and it is necessary that* the control grid rbias be more positive than this value in order for tube 134 to conduct and provide an output corresponding to the electrical pulses induced in coil 135. Thus, only when the selector registers 142 and 143 cornprised of flip-flops U9-U12 and U13-U16, respectively, are arranged so that Ch0 Hd0 is at the effective potential of +125 v. D.C. will tube 134 conduct. It will be noted that when Ch0 Hdl) is effective, Ch0 Hdl, `Ch0 Hd2 Ch9 Hd9 are at the ineffective potential of v. D.C.; however, all of these points are connected to gating unit 104 via line 127 (Fig. l). As shown in Fig. 6, the output of all the gating tubes is present at common junction 136, although, as indicated, the output of only one tube at a time is effective. As already outlined previously in connection with the arc address channel, for example, pulses appearing at junction 136 are amplied, clipped, clamped between the limits +100 v. D.C. and v. D.C., by means indicated generally by the block 128a in Fig. 6, and applied as' grid inputs to memory read nip-flop Mc in synchronismrwith clock proposition C. Y

As shown in Fig. l, output signals from lclock line 126, clock'counter 102, program counter 105, gating unit 104, arc address line 133, and the read heads of recirculating registers H and G are fed into arithmetic unit 103. More specifically, arithmetic unit 103 may be simultaneously receiving corresponding digits of words recorded in one of the storage registers of a memory channel and the digits of words in the H and G recirculating registers. It is the function of arithmetic unit 103 to manipulate this information to obtain a computational result which is either used for control or for recording into one of the registers on the drum.

Reference to Fig. 1l will now be made to describe how the circuitry of the computer serves to effectively interconnect the ip-op circuits of the arithmetic unit in order to carry out the above function. Here, for instance, is shown diode network 137, which for convenience has been arranged as a component within arithmetic unit 103. Y In the computer, however, the arrangement is otherwise in that diodenetwork 137 cannot be regarded as one integral component. Actually, it pervades all computer components, in that portions thereof are found in practically all other components. In other words, connections such as lines 138, 139, and 140 of Fig. 11 actually are made through portions of diode network 137, thus enabling program counter 105 to properly set up this diode network toV cause components to properly carry out a predetermined computational sequence.

In Fig. 11, it is seen that arithmetic unit 103 receives information from drum 101, mixes and alters this iuformation in accordance with a program specified by program counter 105, and either records this altered information or utilizes it for control purposes. As shown, it is diode network 137, the configuration of which is controlled by program counter 105, which operates in response to the terms generated by the several hip-flops and matrices to generate output propositions H0 and G0, the former of which is stepped into ip-ilop H2 to be recirculated in the H recirculating register as the address of the storage register in the main memory to be communicated with, and the latter of which is stepped into hip-flop G2 to be recirculated in the G recirculating reg-V ister as the contents of the storage register selected. For instance, if program counter 105 has set diode network 137 for normal recirculation, the outputs of Hip-flops H1 and G1 will not be modied and thus will provide inputs to Hip-flops H2 and G2, respectively. In other words, propositions H0 and G0 are identical to the outputs from flip-hops H1 and Gl, respectively. However, for some other computer routines, propositions H0 and G0 may be functions of the output of ip-op Mc as well. The output proposition represented by line 127 carries the selective signal identifying a memory head as outlined in connection with Fig. 6. The cycle of 44 clock pulses (one word period) is determined by clock counter 102 and clock proposition C feeding into the left of diode network 137. As mentioned, these componentsoperate to break up the period of a word so as to render certain circuits effective only during portions of a word. The operation of other components of arithmetic unit 103 is reserved for discussion hereinafter.

" A broad outline of the sequence of operation of the 11 computer for the look-up process will next be presented by reference to Fig. 11. Assume tirst that the programmer (computer operator) had previously recorded a word of information into one of the storage registers of a memory channel and knows the address thereof (i.e., the arc address and the channel address). Secondly, it is assumed that the program counter 105 is controlling the computer for operation such that the H recirculating register and the G recirculating register are set for recirculation by arithmetic unit 103. Thirdly, assume that all computer components are in synchronism as directed by clock counter 102. The programmer desires that information in the selected storage register be routed into the G recirculating register and stored therein for future use. The address of the storage register desired is placed in the H recircnlating register where it recirculates in synchronism with the m2 portion of the arc address channel as illustrated in Fig. 5. All subsequent action involved in the look-upA process is automatically accomplished by the computer and is completed in a time interval equivalent to at most 12 word periods. The action of the program counter 105 in automatically carrying out this look-up sequence, comprises the following: in arithmetic unit 103, a binary-coded excess 3 numeral corresponding to the proper memory channel specified in the m2c portion of the H recirculating register is set up in channel selector register 142, thereby causing the appropriate memory channel line of selector matrix 144 (Figs. 7 and 9) to be high. During the same word period, the arc addresses, as read into the Wc fliplop, are operated upon in conjunction with the m2@ portion of the H recirculating register, as it appears in the H1 flip-dop, resulting in the stepping of a binarycoded excess 3 numeral corresponding to the proper memory head into head selector register 143, thereby causing the appropriate memory head line of selector matrix 144 to be high. Thus selector matrix 144 is arranged to connect the proper head through gating unit 104 to ilip-llop Mc. Simultaneously with this action, decimal units, or D4 portion of the arc addresses, as

- read into the Wc flip-flop from the arc address channel 114 on the drum, are being compared with the m2@ portion of the H recirulating register; and ilip-fiop Nd is triggered false if at least one pair of the corresponding binary digits of each are unequal, thus causing program counter 105 to repeat the look-up sequence, i.e., remain unchanged. However, if there are no inequalities, flipflop Nd is not triggered (i.e., it remains true) and program counter 105 counts, causing a one word period delay, after which-diode network 137 is arranged to cause proposition G to follow .the output of ilip-op Mc. Thus the content of the desired arc is withdrawn and routed into the G recirculating register.

Before considering the features of the computer circuitry concerned with the present invention, the convention of the logical methods employed herein, as well as some typical arithmetic techniques, will first be broadly outlined.

Logical propositions may be considered to be represented in circuitry by the states assumed by bistable state circuits having two input lines and two output lines. The arrangement of such a bistable state circuit as used in the present vinvention will be explained by reference to Fig. 12. This circuit is designated as flip-ilop K3 and its function in the circuitry of the present invention will be described hereinafter. This flop-flop circuit utilizes a pair of triode tubes such as tube 129 and tube 130. When a ip-op is in the condition such that tube 130 is cut ott and tube 129 is conducting, it is considered to be true (or the ip-op is said to be storing a binary l). When the hip-opis in its other condition wherein tube 130 is conducting and tube 129 is cut off, it is considered to be false (or the flip-flop is said to be storing a binary 0). Regardless of the state of the flip-flop, it

Awill/generate two terms, one high and the other low.

" going puls'e.

These terms are represented by the iiip-op output lines which are connectedvto the plates of the tubes and which are shown clamped at two operating potentials, v. D.C. and +100 v. D.C. by diodes such as diodes 152 and 153connected to the output line of tube 130. When the flip-hop is in a true state, the output line connected to tube is at +125 v. D.C. while the output line connected to tube 129 is at +100 v. D.C. Similarly, when the ip-op is in a false state, the output line connected to tube 129 is at +125 v. D.C., and the output line connected to tube 130 is at +100 v. D.C. In order to trigger the flip-flop, signals in the form of negativegoing pulses are applied thereto on separate input lines coupled to the grid of each of the flip-Hop tubes in accordance with the convention that the grid of tube 130 must be pulsed in order to trigger the ilip-op into its true state, and that the grid of tube 129 must be pulsed in order to trigger the ip-flop into its false state.

The nomenclature employed herein uses the combination of a capital letter followed by a numeral or small case letter for designating a proposition ip-ilop (K3, B1, Nd, etc.). The output of the flip-dop which is at the high D.C. voltage (+125 v.) when the proposition is true is characterized by the corresponding capital letter with the numeral or small case letter as a subscript (K3, B1, Nd, etc.); and the output which is at the high D.C. voltagek when the proposition is false is similarly characterized except that a prime is aflxed (K3, B1', Nd', etc.). The true input of the ilip-op, i.e., the one which, when energized, renders the proposition true, is characterized by the corresponding small case letter with the associated numeral or smallA case letter as a subscript (k3, b1, nd, etc.); the false input, i.e., the one which, when energized, renders the proposition false, is characterized similarly except that a subscript zero is prexed (0kg, Dbl, 0nd, etc.).

Describing the K3 flip-hop arrangement of Fig. 12 in greater detail, as shown, triodes 129 and 130 are arranged such that the plate of each is intercoupled to the grid of the other by a resistor in parallel with a capacitor, such as resistor and capacitor 146. Each plate is provided with a separate load resistor, such as resistor 147, prior to connection to +225 v. D.C.; each grid is provided with a separate grid resistor, such as resistor 143, prior to connection to -300 v. D.C. bias; and each cathode is grounded. The input to the grid of triodes 129 and 130 is from gating circuits 131 and 132, respectively. The gate outputs are diierentiated and clipped, as for instance by differentiating circuit 149 and diode 150 associated with the grid of triode 129, such thatV negative pulses only are applied to the grids. The output from each triode is from the plate and is clamped between +100 v. D.C. and +125 v. D.C. by crystal diodes, as for example diodes 152 and 153 connected to the plate output of triode 130.

As previously pointed out, the flip-flop circuit is triggered into its opposite state by applying a negative pulse to the grid ofthe conducting tube. If, for instance, the term K3 is to be effective, it is necessary that the plate of triode 130 be high in potential. For this condition to attain, triode 130 must be cut off. Thus it is necessary to apply a negative pulse to the grid of triode 130 by providing an output from gate 132 (i.e., all of the terms DPo, K1, PC-Tf, and C must be simultaneously high). At the end of the pulse period, clock proposition C will become low and the trailing edge of the clock pulse, after differentiation, will produce the requisite negativelt follows that flip-flop K3 will enter pulse position DGPI in a true state. It should be noted that if llip-op K3 were already true during DPO, triode 130 would already be cut oil and the negative pulse supplied by gate 132 would have no effect. In this case, the only way to change the state of ip-ilop K3 would be to pulse the grid of triode 129 by providing an output from gate 131.

The action of flip-hop K3 will be further explained by the waveforms of Fig. 14. These graphs show how ipflopK3 is triggered true from a prior false condition at the end of the time DGPO. Line I represents the clock proposition C` It will be noted that a clock period is measured from the trailing edge of one clock pulse to the trailing edge ofthe succeeding clock pulse. Lines 1I and III show the states of the pulse counter 124 and digit counter 125, respectively, which together define the period DGPD during which diode network 137 is arranged by program counter 105 to make ip-,op K3 responsive to clock proposition trigger pulses which will take effect provided tlip-tlop K1 is true. It is seen that only during the latter half of the DSPO pulse period is the clock proposition C high. In line IV, flip-flop K1 is shown to be false except during the DGP@ period. It is thus during the latter half of the DGPQ pulse period that an elective true input k3 in line V will be generated. However, llipop K3 will be v,triggered true only by a negative-going pulse applied to its true grid. This pulse occurs, as shown in line VI, when the k3 input sharply drops to the low potential at the end of D6P0. The small positive-going 'pulse at the beginning of the second half of DaPo has no eifect on Hip-ilop K3 since tube 130 (Fig. 12) is already saturated. Thus, as line VII shows, the output K3 swings to a high potential at the beginning of period D6P1 and flip-flop K3 will remain in the true state until triggered false at the end of a subsequent DPo period.

As previously stated, the computer logical operations are represented in the form of logical equations using the notation of Boolean algebra. A logical equation for the grid triggering of a ip-tlop circuit consists of stating the terms which have to be eifective, i.e., of a high potential during a clock period, in order that the ip-flop 4circuit will trigger into a particular state at the end of the clock period. Two operations are used in forming the equations. The first, logical multiplication, means that all the terms in the particular product have to be of a high potential in order to make that product effective in a particular equation, and is accomplished in a circuit known as a gate The second, logical addition, means that at least one term of the sum has to be of a high potential in order to make that sum effective in a particular equation, and is accomplished in a circuit known as a mixen Logical gates and mixers will next be described by reference to Fig. 26, which shows ipilop Nd, its triggering equationsA and circuitry.

Thus, for example, the equation:

is interpreted as meaning that the Nd ip-op will be triggered into the false state at the end of the clock period C during which the terms D4 and (Wc'Hr-i-WcHi') are at a high potential, where i (Wc'Hli-WcHl') itself will be of a high potential whenever both theterms Wc' and H1, orboth the terms Wc and H1 are simultaneously of a high potential.

Fig. 26 also shows the logical networks, namely, product networks or and networks, such as 156, which are used to generate the trigger equations for flip-flop Nd.

vProduct network 156 is comprised of` Va pair of input crystal diodes 157 and 158 joined to a common junction 159 connected through a resistor 160 to the positive 1li Vpotential source of 225 v. These diodes are orientated such that whenever the input signals on both diodes are at the high potential of +125 v., the output 161, connected to common junction 159, is at the high potential of +125 v. Any time one or both of the diodeinputs have the low signal potential of v. thereon, output A161 is at this low signal potential.

Output 161, it is seen, comprises one input to a logical sum network 162. This sum network or or network is comprised of a pair of input crystal diodes 163 and 164 joined to a common junction 165 which is returned to ground through resistor 166. These diodes are orientated so that whenever the signal on either one of the inputs is at the high potential of v., the output 167 of the sum circuit, connected to the common junction 165, is at the high potential of +125 v. When neither of the inputs is high in potential, the output 167 is at the low potential of +100 v.

Referring again to Fig. 11, here it is indicated by block 154 that a series of flip-hops, A13 through A16 and iiip-iiop K1, are arranged as an arithmetic adder during D4 5 which receives outputs from ip-fiops Wc and H1.

vAdder flip-flops A13-A16 receive simultaneously only a single pair of equal-order binary digits of the addend, as represented by the signals on output We (complement of We) of the Wc ip-flop, and the augend, as represented by signals on output H1 of the H1 Hip-op. At the end of a clock pulse the least significant (lowest order) digits of each numeral are added and the digits ofthe sum are set up in flip-Hop A13 while the carry is manifested bythe state of tlip-ilop K1, true for a carry and false for no carry. At the end of the next clock pulse period, this sum digit is transferred to Hip-hop A1\4;,and vthe sum of the following digits of each numeral, together with the carry in flip-flop K1, are set up in the A13 ip-op. The addition process is continued until the eightbinary digits of both numerals occurring during D., t,l have been added such that the sum is contained in adder ip-ops A13-A16 with the most significant binary digit in flip-op A13 and the fourth most significant binary digit in flip-flop A16 and a possible carry is held in iiip-iiop K1. Thus, eight clock pulse periods are required to add the two four-place binary numerals Wc and H1.

As noted further in Fig. 11, within the dashed block n155, the A13-A16 flip-ops are again shown similarly arranged during D6 as a fixup adder along with the K2 flip-flop operating as a carry generator. Thus, as is well known in the prior art, in order to serially add two binarycoded excess 3 numerals, two addition processes are resorted to. Y

Reference to Figs. 15, 16, 17, 18, and 19 will serve to further illustrate the operation of the A13-A16 flip-flop circuits. In Fig. 15 is presented a block diagram of flipflops A13-A16 with the logical equations governing their operation set forth below in accordance with the convention already outlined. From the block diagram it is seen that cach of these Hip-flops is'triggered by a clock pulse provided that during the clock period one of the two grid gates is open, i.e., that the grid equation is effective. For instance, flip-hop A14 will be triggered true by the trailing edge of a clock pulse which occurs when the output A13 of ip-ilop A13 is high: a14=A13C. Similarly, ilipflop A14 will be triggered false by the trailing edge of a clock pulse which occurs when the output A13 of ip-tlop 'A13 is high: 0a14=A13'C. In other words, these equations state that the status of ipdiop A14 follows that or" flipop A13, that is, the content of ip-ilop A13 is stepped into Vilip-llop A14 on successive clock pulses. The equa- -tions for flip-flops A15 and A16 complete the ow of information from flip-op A13 to Hip-flop A16 during two additional clock pulse periods. It is seen that i11- formation stepped into flip-flops A14, A15, and A16 comes from the preceding flip-op of the group, that the adder register can be entered from an external source Beamer only via the grid gates of flip-flop A13,vandv that information can be obtained from the register only `from the plates of iiip-flop A16.

The nature of the information set up in flip-flop A13 will now be discussed by reference to 4the D45 term of the iiip-flop A13 equa-tion in Fig. 15 and to the D4 5 table in Fig. 16. During the D4 5 period, the adder register is arranged by program counter 105 such that input to flip-flop A13 is from four different sources: clock proposition C, and flip-liops Wc, H1, and K1. The truth table of Fig. 16 shows the possible states of the three latter sources and indicates that the differentiated pulse derived from the trailing edge of a clock pulse will trigger flip-iiop A13 true for the states of lines I, IV, VI, and VII of the table. This is symbolically represented by the :113 equation shown below the table ofFig. 16. Similarly the differentiated pulse derived from lthe trailing edge `of a clock pulse will trigger flip-flop A13 false for the states of lines II, III, V, and VIII of the table. This is symbolically represented by the am equation shown below the table of Fig. 16. For example, line VI of the table shows that flip-flop A13 is triggered true by the trailing edge of a clock pulse which occurs when the terms We, H1', and K1 are high, which is symbolically Vrepresented as: a13=WH1K1C. It will be further noted on line VI, for example, that since this addition does not produce a carry, and since the carry flip-flop K1 previously was storing a carry, flip-flop K1 must be triggered ifalse a-t the end of this clock pulse period: 0k1=WCH1C. It is in this way that the equations for enabling flip-flop A13 to function as an adder during D4 5 are derived.

As previously indicated in Fig. 11 by means of the dashed block 155, iiip-ops A13-A16, after employment in the adder register during D4 5, are used, in conjunction with flip-flops K2 and K3, as a fixup adder register during D6. It has been pointed out that addend Wc and augend H1 are both binary-coded excess 3 numerals. It is well known that the addition of two excess 3 numerals produces an excess 6 sum. Here the sum contained in iixup adder flip-flops A13-A16 is a binary-coded excess 6 numeral representing the next memory head to be passed by the desired arc and must be converted to excess 3 form for proper manipulation by the computer. This conversion is accomplished by the iixup adder register which receives the excess 6 numeral and performs a computation therewith, thus converting it to the excess 3 form. This computation effectively comprises an addition with the excess 6 numeral as augend and one of two iixup numerals as addend. The choice of iixup addend is determined by the state of adder carry flip-iiop K1 at time DSP@ and the selected fixup addend is formed during the time from DGPI -to DGPS by fixup carry flip-flop K2 and fixup decision flip-flop K3.

The logical equations defining the trigger inputs for iiip-iiop A13 and the carry flip-nop K2 to perform this fixup addition are obtained from the tables shown in Figs. 17 and 18 in a manner analogous to that described in connection with Fig. 16. The composite trigger input equation for the A13 flip-flop, taking into account both adding processes, is shown in Fig. 15, and the circuitry which generates -thetriggering equations for dip-flops A13 to A16 is shown in Fig. 19. The block diagram of carry flip-flop K1 and the circuitry for generating its trigger equations are shown in Fig. 20. Similarly, the block diagram of iiip-iiop K2 and lthe circuitry rfor generating .its `trigger equations are shown in Fig. 21. The nature of these equations will be explained in detail in 'the ensuing description.

Reference will next be made to Fig. 22, which is a portion of the computer flow diagram relevant to the look-up ularaddress specified in the H recirculating register, withdraw the information contained therein, and transfer this information to the G recirculating register for use in subsequent operations. As already pointed out, all sequential one-word-period steps into which computer processes are divided by program counter are characterized by the effectuating of particular circuitry.v Each such step is represented in the ow diagram by a block identified by a number, such as PC#6, and diagrammatically stands for a set of logical operations to be serially performed by diode network 137 on information passing through arithmetic unit 103 during the particular word period. There is a PC# to correspond to each of the output signals generated by the program counter register N1-N9`already described, and a different PC# is Vassigned to each configuration although it may be identical to other prior or subsequent configurations. It follows that the look-up process embodied in PC#6 of Fig. 22 is repeated numerous times in the complete computer flow diagram although `a different PC# may be assigned it each time.

A broad outline of the sequence of operation of the computer look-up process has already been given. There it was assumed that the programmer had previously recorded a word of information into one of the storage registers of a memory channel. It should be understood that the look-up process was employed to do this and thus it follows that the look-up process is essentially the same for recording information into the memory as for withdrawing information therefrom, i.e., the sequence of PC-# is relevant to recording as well as to reading. Initially, when the computer had been energized, the program counter output provided for an idle operating `condition, PC#0; and, after the word is recorded, the computer returns to and remains in, i.e., continuously repeats the sequence of operation ,of PC#0. When the programmer records the address of' the storage register containing the word into the H register, program counter 105 causes the computer to advance from PCi/I0 through a testing sequence, PC#1 to PC#5 (not relevant here), to PC-# which defines the look-up process. In PC#6, aS will be detailed, the memory is searched, the proper memory head identified and its output gated into gated unit 104,V and Athence to iiip-iiop Mc, which thus follows the head output. This condition is maintained for the additional word period of PC#7, employed as a delay to permit switching and other circuit transients to settle. During the following word period (PC#8), diode network 137 isl arranged to transfer the output of flip-flop Mc into the G recirculating register.

As Fig'. 22 indicates, within the rectangle representing each word time block, vconcise statements appear defining the activity during that word period. Below each of the blocks, logical equations are presented which define how the statements made within the rectangle are precisely stated in terms of the computer.

The computer operates on the D44, portions of the address in the H recirculating register together with the arc addresses serially read into ip-liop Wc from the arc address channel during D4 5 in order to set up the head selector register 143 in accordance with a binary-coded excess 3 numeral representing a memory head, and also to determine the word period during which the output of the selected head is gated through to arithmetic unit 103. Subsequently, the computer operates on the D6 portion of the address in the H recirculating register in order to set up the channel selector register 142 so that the selected head on the proper memory channel will be gated through. The flow diagram of Fig. 22 clearly reveals how the main operations performed by the computer to perform the look-up operations are carried out during the word period that PC#6 is effective.

Since the H recirculating register contains the address, of the storage register desired, it is set for recirculation as shown by equation H0 =H1 so that this information will 

